Method of making a dental prosthesis

ABSTRACT

A denture is formed by a rigid acrylic resin tooth-bearing support element and an underlying cushion element of soft thermoplastics material. The cushion element and the support element are interlocked by the process of the invention, which entails sticking irregularly shaped thermoplastics granules on the outer surface of the preformed cushion element, and then pressing the latter into the preformed support element, before the latter is polymerized. The subsequent application of heat melts the granules to form integral undercut appendages on the cushion element, and also polymerizes the acrylic resin, hardening the support element and thereby interlocking the two elements.

United States Patent Gavazzi 51 May 2,1972

[54] METHOD OF MAKING A DENTAL PROSTHESIS [72] Inventor: Leo Gavazzi,Via ltalia 13, Biella, Italy [22] Filed: Dec. 7, 1970 [21] Appl. No.:95,780

Primary Examiner-Robert Peshock Attorney-Sughrue, Rothwell, Mion, Zinn &Macpeak [5 7] ABSTRACT A denture is formed by a rigid acrylic resintooth-bearing support element and an underlying cushion element of softthermoplastics material. The cushion element and the support element areinterlocked by the process of the invention, which entails stickingirregularly shaped thermoplastics granules on the outer surface of thepreformed cushion element, and then pressing the latter into thepreformed support element, before the latter is polymerized. Thesubsequent application of heat melts the'granules to form integralundercut appendages on the cushion element, and also polymerizes theacrylic resin, hardening the support element and thereby interlockingthe two elements.

5 Claims, 5 Drawing Figures PATENTEDMM 21922 3, 659,344

INVENTOR 1 50 GA VA .2 Z/

ATTORNEY5 kacftn-K v BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to the manufacture of a dentalprosthesis, or, as it is commonly called, a denture, more particularly adenture of the type formed by a tooth support element of rigid resin,generally acrylic resin, and a cushion elementof flexible resin attachedto the underside of the support element. The purpose of the cushionelement is to avoid bruises to the mucuse of the gums, and to assistsecure and stable fitting of the denture in the wearers mouth.

2. Description of the Prior Art Italian Pat. No. 783,475 relates to aprocess for the manufacture of dentures of the above mentioned type,which con sists in arranging the rigid element of acrylic resin in amould, forming in the mould a space for the cushion element, fillingthis space with thermoplastic flexible resin and heating the mould so asto'keep the thermoplastic resin in a molten state, while exertingsimultaneously a pressure on the thermoplastic resincontained in themould by injecting further molten resin of the same type from theoutside, thereby forming the cushion element.

According to this process the rigid element of the denture in acrylicresin is placed in the mould in a soft state prior to polymerization,while the thermoplastic resin is used in a solid state, in prefabricatedsheet or powder form, to till the space obtained in the mould; in thisway the heating of thernould produces the softening of the thermoplasticresin and the simultaneous polymerization of the acrylic resin.

It is therefore necessary to employ for the formation of the softcushion element a flexible thermoplastic resin which has a meltingtemperature which is not greater than the polymerization temperature ofthe acrylic resin.

This latter process has, however, some practical disadvantages, duemainly to the difficulty of effecting a firm connection between theelements of the denture, especially having regard to the high pressurewhich the denture itself has to bear in use.

SUMMARY OF THE INVENTION An object of this invention is to avoid suchdrawbacks by providing a process for the manufacture of dentures of theaforesaid type, which is both simple and economical and which producesdentures having two-elements formed of different resins andinterconnected in a strong and secure way, resistant to pressures towhich the denture itself is subjected in use.

' Another object of this invention is to provide a process which allowsmanufacture of dentures of the above mentioned typewhich are of longduration and comfortable in use.

More specifically, it is an object'of the invention to provide a processfor the manufacture of a denture of the aforesaid type, comprising thesteps of: forming a cushion element of soft thermoplastic resin;separately pre-forming a tooth support element in acrylic resin in asoft state; sticking a number of small irregularly shaped granules ofthe same material as that forming the cushion element on that surface ofthe preformed cushion element which mates with the support element;pressing the two elements together, to cause the granules projectingfrom said surface of the cushion element to penetrate into the supportelement while the acrylic resin of the latter is still in a soft state,and subsequently heating the two elements and holding them togetherunder pressure while the thermoplastic resin which forms both thecushion element and the granules melts, the granules forming integralappendages on the cushion element and the heat polymerizing the acrylicresin of the support element and rigidifying the latter, therebyincorporating said appendages, integral with the soft cushion element,in the resin of the rigid support element and interlocking the twoelements.

The invention also comprehendsa denture manufactured by the aboveprocess, comprising a soft pre-formed cushion element of thermoplasticmaterial anchored to a rigid support of the denture teeth throughintegrally-formed appendages on the cushion element, of the samethermoplastic material as the latter, which project from one surface ofthe soft'cushion element and penetrate into the rigid support element.

BRIEF DESCRIPTION OF THE DRAWINGS Further characteristics and advantagesof this invention will be apparent from the detailed description whichfollows, given by way of non-limiting example, with reference to theappended drawings, in which: 7

FIG. 1 is a diagrammatic transverse cross-section of one element of adenture, illustrated in a first phase of the process of manufactureaccording to this invention;

FIG. 2 is a transverse cross-section of the element illustrated in FIG.1, in a-second phase of the process;

FIG. 3 is a transverse cross-section of the two elements of the denturein a third phase of the process, and

FIGS. 4 and 5 similar tov FIG. 3, illustrate respectively a furtherintermediate phase of the process.

DESCRIPTION OF THE PREFERRED EMBODIMENT v cushion element and a rigidtooth support element 3 (FIG. 3).

The cushion element 1 is pre-formed separately, for example, by a lostwax technique. According to this well-known technique, the cushionelement 1 is prefabricated in thermoplastic flexible synthetic resin, byfilling a mould first with wax and subsequently dissolving the wax inhot water; the space previously filled by the wax is then filled withmolten thermoplastic resin to form the cushion element 1" (FIG. I). Theresin is injected under pressure by a piston-press of small diameter, ofthe type normally used for pressing thermoplastic resins. I I I I Theouter surface of the cushion element 1 is adapted to mate with thesupport element of the denture, by consecutively distributing on thesaid. outer surface a larger number of small irregularly shapedparticles, in this example small misshapen granules 2, whose maximumsize does not exceed 0.5 mm. The granules 2 are obtained by grinding thesame material as thatfrom which the soft. cushion element 1 is formed. I

The granules 2 are spread on the outer surface of thecushion element Iafter suitable adhesive has been applied to said surface. The granules 2remain-attached to the flexible cushion element I and can be applied tothe element 1 in the desired quantity and at the most suitable positionson the outside surface of the latter, as illustrated in FIG. 2.

The cushion element 1 so prepared is inserted in one half of a mould(not shown) into which an acrylic resin which forms the support element3 has previously been pressed, while still in a soft, pliable, or doughystate (see FIG. 3).

For example, the two elements 1, 3 of the denture may be pressedtogether in a screw press as illustrated in FIG. 4, so as to cause thepenetration of the irregular granules 2 attached to the cushion element1 into the still soft acrylic resin which forms the support element 3.

During this pressing phase the granules 2 remain attached to theflexible cushion element 1. Heat is then applied to the two elements 1and 3 while the thermoplastic resin of the soft cushion element 1 is putunder pressure by means of an injector or small diameter screw-piston.

With the application of heat all the thermoplastic resin melts,including the granules 2 which are of the same material It will beappreciated that details of specific embodiments of this invention canbe widely varied from the embodiment which has been described andillustrated, without departing from the scope of this invention.

I claim:

1. A process for the manufacture of a denture of the type formed by arigid tooth support element and a cushion element of soft plasticsmaterial permanently attached to the underside of the rigid supportelement, said process comprising the steps of:

preforming-a cushion element of soft thermoplastic resin; separatelypreforming a tooth support element in acrylic resin in a soft state;providing a number of small irregularly shaped granules of the samematerial as that forming the cushion element on that surface of thepreformed cushion element which mates with the support element; pressingthe two elements together, to cause the granules projecting from saidsurface of the cushion element to penetrate into the support elementwhile the acrylic resin of the latter is stillin a soft state; heatingthe two elements and holding them together under pressure while thethermoplastic resin which forms both the cushion element and thegranules melts, the granules fonning integral appendages on the cushionelement and the heat polymerizing the acrylic resin of the supportelement and rigidifying the latter, thereby incorporating saidappendages, integral with the soft cushion element, in the resin of therigid support element, and

cooling the two elements to interlock them together.

2. A process as in claim 1, where the granules are adhesively applied tothe cushion element.

3. A denture comprising a rigid tooth-carrying support base of athermosetting plastic, and

a soft cushion element of thermoplastic material having projectingappendages of the same thermoplastic material. the projecting appendagespenetrating into the thermosetting plastic support base to form apermanent interlocking between the support base and the cushion element.

4. A denture as in claim 3, where the penetrating ends of the projectingappendages are larger than the ends attached to the cushion element,whereby the support base and the cushion element are permanentlyinterlocked.

5. A denture as in claim 4, where the projecting appendages have amaximum thickness of 0.5 mm and the thermosetting plastic is an acrylicresin.

2. A process as in claim 1, where the granules are adhesively applied tothe cushion element.
 3. A denture comprising a rigid tooth-carryingsupport base of a thermosetting plastic, and a soft cushion element ofthermoplastic material having projecting appendages of the samethermoplastic material, the projecting appendages penetrating into thethermosetting plastic support base to form a permanent interlockingbetween the support base and the cushion element.
 4. A denture as inclaim 3, where the penetrating ends of the projecting appendages arelarger than the ends attached to the cushion element, whereby thesupport base and the cushion element are permanently interlocked.
 5. Adenture as in claim 4, where the projecting appendages have a maximumthickness of 0.5 mm and the thermosetting plastic is an acrylic resin.